Threat Explorer

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29 May 2003
13 February 2007
Systems Affected:
Mac, Windows

O97M.Cian.D is a macro virus that infects documents created in Microsoft Word 97 and later, as well as spreadsheets created in Microsoft Excel 97 and later. The virus creates a Trojan Horse that drops a batch file virus.

There have been no reports of this virus in the wild.

O97M.Cian.D infects Microsoft Word 97 and Microsoft Excel 97. It also infects the Microsoft Word template file, and in Excel, it creates Personal.xls in the XLstart folder.

The payload of the macro is the creation of the MSTnglnk.exe file, which is a batch file virus. The infection module is named "TANG."

When O97M.Cian.D is run, it does the following:
  1. Creates the file, %System%\MSTnglnk.exe.

    NOTE: %System% is a variable. The virus locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. Then, MSTnglnk.exe drops itself as any number of 22 byte executables in the %System% folder.

  3. MSTnglnk.exe adds a line to all the .bat files to run itself, thus perpetuating the infection of all the batch files. MSTnglnk.exe and its clone files are detected as Trojan.Cian.

  4. Disables the Macro security in Word and Excel.

  5. Disables access to the following menus:
    • Tools > Macro
    • Tools > Customize
    • Tools > Macro > Security
    • View > Toolbars

  6. The macro imports and exports its code using %Windir%\MSTngmgr32.ocx.

    NOTE: %Windir% is a variable that describes the Windows installation folder. By default, this is C:\Windows or C:\Winnt).

  7. The macro creates the following registry key to verify that MSTnglnk.exe has been dropped:


    If the value is "1," then the macro will no longer drop the Trojan Horse file.

When the macro is run from an infected Word document, it creates an infected Personal.xls in the XLStart folder. The macro does not infect from Excel to Word.

NOTE TO MACINTOSH USERS: The macro does infect documents and spreadsheets when running Microsoft Word and Microsoft Excel on a Macintosh computer, but the Trojan creation does not successfully run.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan and repair all the files detected as O97M.Cian.D. Delete %Windir%\MSTngmgr32.ocx.

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Anti-Virus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Scanning for and repairing the infected files
  1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with O97M.Cian.D, click Repair.
  4. Using Windows Explorer, locate and delete %Windir%\MSTngmgr32.ocx.

Writeup By: Maryl Magee